Yucca 'Bronze Age' is a blue-green yucca that has deep burgundy bronze colouration in fall and winter.

Yucca filamentosa 'Excalibur' forms rosettes of spiky, strap-like leaves coloured blue-green to powdery blue.

Yucca filamentosa 'Hofer's Blue' forms rosettes of spiky, strap-like leaves coloured in a bold silver-blue.

Zanthoxylum piperitum, the Japanese pepper, is an aromatic, spiny shrub with small, yellowish green flowers and scarlet fruits used in Japanese and Korean cooking.

Zanthoxylum simulans, the Sichuan pepper, produces brownish red fruits that are used in Sichuan cuisine having a spicy, numbing effect.

Zinnia grandiflora 'Gold on Blue' is hardy to zone 4 with fine, textured, bluish-green foliage topped with golden yellow flowers all summer.